The National Health and Nutrition Examination Survey is an on-going, national, comprehensive health survey of the civilian, non-institutionalized US population. A vision assessment was added in 1999 and is on-going. All sample persons aged 12+ years undergo a vision assessment in which measures of the eyeglass prescription in people who wear glasses for distance, tests the distance visual acuity of sample persons with and without correction (glasses/contacts) and an objective refraction (incorporating also an evaluation of the corneal curvature of the eye) are obtained. A visual acuity at near is assessed in persons age 50 years and over. In addition, personal interview data on functional measures related to vision are collected on people over the age of 19 years (prior to 2005, these data were collected only from those 50 years of age and older). Data from the vision component in NHANES will be used to estimate the prevalence of visual impairment in the U.S. population, describe the distribution of refractive error in the U.S. population, evaluate the impact of vision loss on functional abilities, and relate visual impairment to other health and disease measures. The prevalence data will be used as baseline measures for a vision objective in Healthy People 2010. Data collection is on-going. The vision interview protocol has been further refined to better assess the frequency of severe visual impairment, particularly as it relates to those who, for various reasons, subsequently do not participate in the vision examination component as conducted in the mobile units. Vision data, collected between 1999 and 2002, were publicly released by the National Center for Health Statistics for analytic purposes in spring 2005.